Push-pull high frequency stage



June 10, 1941. SCHRUMPF 2,244,807

I. PUSH'PULL- HIGH FREQUENCY STAGE Filed Nov. 29, 1938 2 Sheets-Sheet 1 FIG.3.

INVENTOR MAX SLHRUMPF ATTORNEY J1me 1941- M. SCHRUMPF 2 4,

PUSH-PULL HIGH FREQUENCY STAGE Filed Nov. 29, 1938 2 Sheets-Sheet 2 INVENTOR MAX SCHRUMPF ATTORNEY Patented June 10, 1941 PUSH-PULL HIGH FREQUENCY STAGE Max Schrumpf, Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof,

Germany, a company Application November 29, 1938, Serial No. 242,912

In Germany November 10, 1938 Claims.

The invention relates to the electric and apparatus arrangement of push-pull connected high frequency stages for use with very short waves, namely waves in the order of magnitude of some meters or still shorter, and is especially intended for push-pull connected stages employed in high frequency transmitters.

In the accompanying drawings, Fig. 1 is a wiring diagram showing a known arrangement of this kind, Fig. 2 represents one embodiment of the invention, and Fig. 3 is a bottom plan view of the arrangement represented in Fig. 2.

Two push-pull connected tubes I, 2 have a heating or cathode circuit common to them and to which the heating voltage is supplied at H. To the grids of these tubes a voltage is supplied in phase opposition from a pre-stage or a control stage over terminals 4 and a coil 5. Condensers 6, I serve in well known manner the purpose of de-tuning. In addition, the grids are joined at G to a source of biasing potential. Included in the anode circuit is an inductance composed of coils 8, 9 and coupled through a coil III to a utilization circuit or an additional amplifying circuit. The anode voltage is supplied at +A over choke coils. Condensers II, I2 are in well known manner arranged as neutralizing means. Circuit 3 is symmetrically tapped in high frequency fashion by condenser I3 and is tapped in low frequency fashion at resistance I4 while being connected by a line I5 with an earthed metallic screening or mounting plate I6.

When assembling this arrangement, which is well known per se, a number of difliculties arise in the case of very high frequencies. In fact, with these frequencies the tubes I, 2 employed in practice are of the kind in which the cathode leads are mounted in a socket provided at the lower end of the glass bulb while the anode connection is provided at the upper end thereof. The grid connection is arranged say in the middle between the cathode and anode connections, the leads of these thus projecting laterally from the bulb. In the operation of such tubes a drop of potential arises across the intervening air space because of stray capacity effects, the grid connection together with the grid circuit lying in the field of said potential. As a result, undesired high frequency voltages are applied to the grid connection, whereby retroactive coupling phenomena can take place.

In accordance with the invention this disadvantage is overcome by avoiding the tubes I, 2 being mounted directly on plate I6. The invention provides for arranging them in such manner that the grid leads are somewhat upon the level of plate I6, this being of zero potential. In this way the cathode leads will be located below plate I 6 while the anode leads will be above this plate, the level of the grid connection then acting as neutral point, that is, as a point of no voltage. Undesired voltages are thus prevented from influencing the grid.

Another disturbing influence is due to the line It by which the symmetric cathode point is connected with the metal plate I6 earthed in direct current fashion. Owing to the aforesaid high frequencies line I5 is of considerable inductance. This inductance acts to couple the tube stages to each other, such being the case especially if several stages of the kind shown in Fig. 1 are comprised in one apparatus.

In order to avoid this disadvantage the invention proposes to arrange the heating conductors of tubes I, 2 in such a manner that they are independent of one another until they reach the plate I8, and directly at this place to obtain by means of condenser I3 the symmetry effected in high frequency fashion. In this way the two cathode circuits will have no conductor common to them in high frequency fashion, coupling phenomena thus being avoided to a considerable extent.

In Figs. 2 and 3 the same reference numerals are used as in Fig. 1. In accordance with the invention the grid connections II, I8 of the tubes I, 2 are located on the level of the earthed metal plate IE, or nearly so. The anode connections are denoted by I9, 20 while the tube sockets, in which the cathode leads are contained, are designated 2|, 22, respectively. The heating conductors are constituted by metal bows 23, 24. These are arranged to extend close to plate I6 and are there at tabs 25, 26 through which the heating voltage is supplied, rendered symmetrical in high frequency fashion by means of symmetry condenser I3. The stationary coatings or armatures of this condenser are joined at 25 tobow 24 and at 26 to bow 23, while the mid-coating thereof is in direct connection with plate I6.

One more influence of disturbing nature has been observed, as will be understood from the following. The electrode system of each tube I or 2 is located in a globular glass body which forms the upper part of the tube. The cathode leads are arranged to extend within a cylindrical portion of the bulb downward to the sockets 2|, 22. Outside the tubes, where the cathode leads are constituted by the bows 23, 24, they extend upward toward plate I6. Therefore those parts of the cathode leads located within the tubes and those located outside thereof form a sort of loop with each other by which undesired voltages may be induced in the grid coil 5.

Under the invention this disturbing influence is obviated by means of metallic screening plates 21, 28 which are directly attached to how 24. These plates may be made inone piece with the bows 24, 24.

What is claimed is:

1. A high frequency stage comprising push-pull connected electron tubes, a metal plate of zero potential, grid leads laterally projecting from said tube substantially on the level of said metal plate, heating conductors for said'tubes extending toward said plate independently of each other, and impedance means for rendering said conductors symmetric with respect to said plate in high frequency fashion, said means being located in close proximity to said metal plate, whereby retroactive coupling in said stage is reduced.

2. A high frequency stage according to claim 1, wherein said impedance means is a condenser having two coatings connected with the heating conductors and a third coating joined to said metal plate.

3. A high frequency stage according to claim 1, wherein the heating conductors are formed as metal bows.

4. A high frequency stage according to claim 1, wherein the heating conductors are formed as metal bows and wherein metal plates are attached to these bows, such metal plates being adapted to screen the heating conductors against the grid circuit.

5. A high frequency stage according to claim .1, wherein the heating conductors are metal bows formed integral with plates adapted to screen the heating conductors against the grid circuit.

MAX SCHRUMPF. 

